Automatic time delay



A ril 19, 1938. D. D. KNOWLES AUTOMATIC TIME DELA) Filed Oct. 21, 1936 INVENTOR Dewey D. Knowles.

ATTOR Y l z Il /I I 11 WITNESSES:

Patented Apr. 19, 1938 PATENT OFFICE AUTOMATIC TIME DELAY DcweyD.

Knowles, Wllkinsburg, 2a., asslgnor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa. a Pennsylvania corporation of Application 0mm :1, 1m. Serial No. 100,100

flOlallns.

My invention relates to circuits including electron discharge devices, and especially to such devices utilizing an oxide coated cathode where a time delay is necessary in establishing the anodecathode discharge until the oxide coating is sufficiently electron-emissive.

This application is an improvement on the circuit arrangements disclosed in the copending application of Erwin F. Lowry, Serial No. 43,347, filed October 3, 1935, for Electron discharge apparatus.

It is an object of my invention to provide means for automatically delaying the establishment of a discharge to an oxide coated cathode when the tube has been recently ignited.

Other objects and advantages will be apparent from the following description, taken in conjunction with the accompanying drawing, in which:

Fig. i is a diagrammatic view of a preferred circuit arrangement, and

Fig. 2 is a view, partially in cross-section and partially in elevation, of a preferred type of tube diagrammatically illustrated in the circuit of Fig. 1.

In the copending application of Erwin F. Lowry, Serial No. 43,347, flied October 3, 1935, is described a tube and circuits therefor designed to provide an automatic time delay member within the tube for the anode-cathode discharge. It is well known that if the anode-cathode discharge is established to an oxide coated cathode before this cathode becomes sufllciently electron-emitting, the discharge will seriouslydamage the coating. This is due to the fact that the positive ions of the gaseous atmosphere meet little opposition in traveling to the cathode. If the cathode is emitting sufllcient electrons, these electrons appear to have a cushioning effect upon the ions so that the oxide coating is not damaged. Prior to the invention of Erwin F. Lowry, described in the above referred to copending application, it was necessary to apply the heating current to the cathode for a certain length of time before applying the anode-cathode voltage or to utilize elaborate and complicated auxiliary apparatus to prevent the establishment of the anode-cathode discharge until the cathode became sufllciently electron-emitting.

The invention described in Erwin F. Lowrys copending application, however, provided automatic means within the tube for providing an automatic time lag for the discharge until the cathode was properly electron-emitting.- This automatic means was substantially a perforated member enclosing the cathode and when cold. having a space charge that prevented the passage of electrons through its openings. The heating current through the cathode heated this member until it became electron-emitting, and when hot, this member permitted the establishment of the discharge. The one difficulty with the tube was that if the tube was reconnected in the circuit almost immediately after the discharge had stopped, the temperature of the member enclosing the cathode and the vapor pressure would not have, decreased sumciently for the member to block the discharge. It is one of the purposes of my invention to provide an automatic temporary blocking charge on this member at the cooling period following a discharge.

In Fig. 2, I have illustrated a tube of the preferred type illustrated in the copending Erwin F. Lowry application Serial No. 43,347. This tube comprises a glass casing it with an anode II and an oxide coating directly heated cathode l2. Surrounding this cathode i2 is preferably a casing ll comprising a perforated metal screen ll.

When the heating current and cathode-anode voltage is applied to the tube, the space charge on the member I will prevent the passage of the electrons therethrough. The heat developed by the cathode I! will raise the temperature of the member it until it becomes electron-emitting, and the space charge disappears, and the cathodeanode discharge is established. Such a type of tube I have indicated at Iii in Fig. 1 with the corresponding anode ll, cathode i2 and perforated member ll diagrammatically illustrated.

The load is illustrated at it in the cathodeanode circuits l6 and i! which is connected to any desired electrical source. I connect a condenser II and a resistance R1 or I! in parallel with the load. The intermediate point Ill between the condenser and this resistance is connected to the control member ll of the tube. In case it is desired to use a protective resistance to prevent burning out of the member It in case of an are between the member I and the cathode,. a resistance R: can be utilized at 2| between these two members.

The desired cooling time of the member ll between its hot emitting state and its cold blocking state is calculated. The product of the capacity of the condenser It in farads and the combined resistance of the load and R1 in ohms is taken as equivalent to the value of the cooling time in seconds.

As an example, suppose the cooling time of screen it is that of five minutes or 300 seconds.

The capacity 01' the condenser may then be taken as a convenient one and the resistance calculated or the resistance taken and the capacity calcu-' then the equationwill be 20x 10- R=300 seconds or R=15 megohms In operation of the device, the discharge will charge up the cathodeplate of the condenser 22 positive and the other plate 23 negative. whenthe discharge stops the negative charge will be applied to the member I and will then gradually leak 01!. as the member it cools to its discharge blocking state.

Accordingly, I have devised a system for placing a temporary blocking charge on the member H, so'that it the tube is reconnected prematurely in the circuit, the discharge will not be prematurely established, but this temporary blocking charge will delay the initiation of this discharge until the cathode I2 is sufllciently electron-emitting to protect its coating from ion bombardment.

with my arrangement the member ll prevents the discharge either when the member I4 is at cathode potential and the vapor pressure is low and the cathode cold, or when the member I4 is negative with respect to the cathode and the tube is hot and the cathode cold. The member H permits the discharge when it is at cathode potential and the cathode is hot with vapor pressure high or low, and also permits the discharge when the member I4 is negative with respect to the cathode and both the tube and cathode are hot. The hot cathode in these last conditions will not be deleteriously ail'ected by the discharge.

, While I have disclosed a preferred embodiment of my invention, it is apparent that many modiflcations thereot are possible. Accordingly, I desire only such limitations on the following claims as is necessitated by the prior art.

I claim as my invention:

1. In combination, a discharge device having an anode and a heatable cathode and an electron emitting member adjacent said cathode preventing a discharge when cold and permitting the vice.

discharge when hot and circuit means putting a temporary blocking charge on said member when the discharge stops.

2. In combination, a discharge device having an anode and a heatable cathode, 'and an electron emitting member adjacent said cathode preventing a discharge when cold and permitting the discharge when hot and circuit means putting -a temporaryblocking charge on said member during the time when said member is cooling from its hot state to its cold blocking state.

3. In combination, a discharge device having an anode and a heatable cathode, and a member adjacent said cathode preventing the discharge when cold and permitting the discharge when hot, and a condenser connected to said member charged by the discharge and applying a blocking charge to said member when the discharge stops.

4. In combination, a discharge device having an anode and a heatable cathode, and a member adjacent said cathode preventing the discharge when cold and permitting the discharge when hot'and a condenser connected to said member charged by the discharge and applying a blocking charge to said member when the discharge stops for the cooling time of said member.

5. In combination, a discharge device having an anode and a heatable cathode, and a member adjacent said cathode preventing the discharge when cold and permitting the discharge when hot, and a condenser connected to said member charged by the discharge and applying a blocking charge to said member when the discharge stops, and a leakage path for said charge for the cooling time of said member.

6. In combination, a discharge device and a circuit therefor, said device having an anode and a heatable cathode and a member adjacent said cathode preventing the discharge when cold and permitting the discharge when hot, said circuit comprising a condenser charged by the discharge and applying a blocking charge to said member .when the discharge stops, and resistance means providing a leakage path for said charge. the capacity of the condenser and the value or the resistance means providing a leakage time tor said charge substantially equivalent to the cooling time of said member or said discharge de- DEWEY D. KNOWLES. 

